Hybrid cars run most of the times with the electrical power and the combustion engine is idle. Since fuel tank is a closed system, thus in general due to evaporation of stored fuel it results in positive pressure inside the fuel tank. Moreover, it is necessary for vehicles to maintain an elevated pressure in the fuel tank to suppress the rate of fuel vapor generation and to minimize hydrocarbon emissions to the atmosphere. The most obvious solution, to overcome the problem is to provide a fuel tank isolation valve (FTIV) coupled to fuel tank to control fuel tank venting. The fuel tank isolation valve (FTIV) may be located in a conduit between a fuel tank and a fuel vapor canister in an evaporative emission control system. It opens automatically when the pressure exceeds protection limits and valve is electrically actuated at the time of re-fuelling.
A fuel tank isolation valve (FTIV) includes, a housing sub-assembly which is generally circular in shape and includes an electrically controlled solenoid valve, a compression spring fixed inside the housing sub assembly to perform over—vacuum relief function, a seal sub-assembly, a guiding shaft coupled with seal sub-assembly for inline guiding of flow limiter, a nozzle body with mounting flanges which is mounted over housing sub-assembly to be connected to the fuel tank and canister of the vehicle, a compression spring fixed over flow limiter to perform over-pressure relief function and a cover which will be mounted over nozzle body to close the valve and maintains the installation height of the compression spring for over-pressure relief function.
In specific application, like in hybrid cars, as the cars drive without the combustion engine running, thus, the gasoline in the tank can evaporate and create a pressure increase in the tank which is controlled by fuel tank isolation valve (FTIV). In such instances the compression spring fixed over the flow limiter allows flow limiter seal to open and release the excess vapors to the canister and maintain the vehicle tank pressure in a protected range.
In case there is a negative pressure or vacuum generated due to falling temperatures (e.g. if a car is parked overnight), fuel tank isolation valve (FTIV) opens automatically and allows vacuum seal to open and connect the fuel tank with canister to maintain the vehicle tank pressure in a protected range.
The fuel tank isolation valve (FTIV) also enables fuel vapor containment in the fuel tank until conditions are appropriate for the engine to process the excess vapor.
At present, conventional fuel tank isolation valves (FTIV), have separate sealing for over-pressure and over-vacuum relief function. Further, a sealing feature is provided in the Nozzle Tank itself to separate the Tank and canister chamber to provide the OPR and OVR sealing separately. This leads to the over dependency on individual parts, while the valve is under operation.
Further, having a separate guide for guiding of over pressure seal and over vacuum seal, there are chances of misalignment after a certain period of operation which may cause leakage and hinder the required performance. Further, this may lead to malfunctioning of OPR and OVR function.
Further, in electric part of conventional fuel tank isolation valve (FTIV), immersion of gasoline is only restricted by the over molding of the solenoid coil and its connection terminals. However, it is a well-known fact and widely accepted that, because of various factors like accumulation of gas around over molded piece and/or inside mold tool, improper raw material, bad surface finish of solenoid coil body part leads to the improper sealing between the plastic molded piece and solenoid coil body jeopardizes the safety of a piece and the overall vehicular safety.
Hence there is a technological gap, wherein there is a need for advancement in achieving low emission vehicle with a robust and leakage proof design of a fuel tank isolation valve (FTIV).